Short guard interval with green field preamble

ABSTRACT

Systems, methods, and other embodiments associated with a single stream wireless communication with a greenfield preamble that uses a short guard interval are described. According to one embodiment, a wireless communication device includes a transmitter configured to generate an orthogonal frequency-division multiplexing (OFDM) signal that comprises (i) a preamble and (ii) a data segment. The data segment follows the preamble. The data segment includes a plurality of data symbols that are each respectively preceded by a corresponding guard interval. A first guard interval preceding a first data symbol in the data segment has a first duration of time and each of the corresponding guard intervals that precede the remaining data symbols subsequent to the first data symbol in the data segment have a second duration of time. The second duration of time is shorter than the first duration of time.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent disclosure is a continuation of U.S. application Ser. No.13/465,347 filed on May 7, 2012, now U.S. Pat. No. 8,873,680 whichclaims priority under 35 U.S.C. §119(e) to U.S. Provisional ApplicationSer. Nos. 61/487,581 filed on May 18, 2011 and 61/563,409 filed on Nov.23, 2011.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventor(s), to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Modern computer systems often use wireless communications to transferinformation between two or more devices that are not physicallyconnected. While wireless communications improve the convenience ofconnecting to a network, wireless communications also introduce manydifficulties. Among these difficulties is interference from the wirelesschannel on which the wireless communications are transferred.

For example, consider a wireless network in which a laptop computer iscommunicating with a wireless access point. One source of interferencemay occur when a signal sent from the laptop arrives at the access pointvia many different paths. These paths may occur as the result ofreflections from walls and other obstacles between the devices. This isknown as multipath propagation and can cause intersymbol interference.Accordingly, wireless computer systems may use techniques to mitigateintersymbol interference. However, these techniques may reducethroughput and cause processing delays.

SUMMARY

In one embodiment, a wireless communication device includes atransmitter configured to generate an orthogonal frequency-divisionmultiplexing (OFDM) signal that comprises (i) a preamble and (ii) a datasegment. The data segment follows the preamble. The data segmentincludes a plurality of data symbols that are each respectively precededby a corresponding guard interval. A first guard interval preceding afirst data symbol in the data segment has a first duration of time andeach of the corresponding guard intervals that precede the remainingdata symbols subsequent to the first data symbol in the data segmenthave a second duration of time. The second duration of time is shorterthan the first duration of time.

In one embodiment, a method includes generating an orthogonalfrequency-division multiplexing (OFDM) signal that comprises (i) apreamble and (ii) a data segment. The data segment follows the preamble.The data segment includes a plurality of data symbols that are eachrespectively preceded by a corresponding guard interval. A first guardinterval preceding a first data symbol in the data segment has a firstduration of time and each of the corresponding guard intervals thatprecede the remaining data symbols subsequent to the first data symbolin the data segment have a second duration of time. The second durationof time is shorter than the first duration of time. The method includestransmitting the OFDM signal over a wireless communication medium usinga transmitter.

In one embodiment, a device includes a transmitter configured togenerate an orthogonal frequency-division multiplexing (OFDM) signalwith a greenfield preamble and a mixed pattern of guard intervals thatincludes a first guard interval in the OFDM signal as a long guardinterval and subsequent guard intervals in the OFDM signal as shortguard intervals. The device includes an interval select logic configuredto control the transmitter to generate the OFDM signal with the mixedpattern of guard intervals when the OFDM signal is a single streamcommunication.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate various systems, methods, andother embodiments of the disclosure. The illustrated element boundaries(e.g., boxes, groups of boxes, or other shapes) in the figures representone example of the boundaries. In some examples, one element may bedesigned as multiple elements or multiple elements may be designed asone element. In some examples, an element shown as an internal componentof another element may be implemented as an external component and viceversa. Furthermore, elements may not be drawn to scale.

FIG. 1 illustrates one embodiment of an apparatus associated withprocessing single stream communications with a short guard interval andgreenfield preamble.

FIG. 2 illustrates example greenfield preamble formats for multi-streamand single stream signals.

FIG. 3 illustrates one embodiment of a method associated with processingsingle stream communications with a short guard interval and greenfieldpreamble.

FIG. 4 illustrates one embodiment of an integrated circuit associatedwith processing single stream communications with a short guard intervaland greenfield preamble.

FIG. 5 illustrates one embodiment of an apparatus associated withprocessing single stream communications with a short guard interval andgreenfield preamble.

FIG. 6 illustrates one embodiment of a method associated with processingsingle stream communications with a short guard interval and greenfieldpreamble.

FIG. 7 illustrates one embodiment of an integrated circuit associatedwith processing single stream communications with a short guard intervaland greenfield preamble.

DETAILED DESCRIPTION

Described herein are examples of methods, devices, and other embodimentsassociated with processing single stream communications that includegreenfield preambles and short guard intervals. Wireless communicationdevices, for example those modulated by orthogonal frequency-divisionmultiplexing (OFDM), use guard intervals when transmitting acommunication to mitigate the effects of intersymbol interference. Aguard interval occurs prior to a data symbol in the communication toprovide time for interference (e.g., multipath interference) from aprevious symbol to dissipate before a subsequent symbol is transmitted.In this way, a transmitting device can avoid creating interference inthe subsequent data symbol by using the guard interval. The guardinterval of a communication may be, for example, short (e.g., 0.4 μs) orlong (e.g., 0.8 μs). A long guard interval can mitigate longerintersymbol interference than short guard intervals. However, long guardintervals consume a greater proportion of a symbol and thus cause alower throughput than a short guard interval that occupies less time.Thus, for different circumstances a wireless communication device canchoose to transmit communications with either a short or long guardinterval. An example of such a system is a wireless local area network(LAN) system compatible with IEEE 802.11n, IEEE 802.11ac, IEEE 802.11af,IEEE 802.11ah standards, and so on.

To notify a receiving device of a type of guard interval and otherconfiguration parameters about a communication, a transmitting deviceincludes a preamble at the beginning of the communication. Accordingly,to properly interpret a communication, a receiving device decodes thepreamble and determines the type of guard interval and otherconfiguration parameters of the communication. However, the receivingdevice may not be able to determine the type of guard interval (referredto herein also as “guard interval type”) before a first data symbol inthe communication is received because decoding the preamble can be atime consuming process that is not completed before the first datasymbol is received.

For example, consider a wireless device that receives a single streamcommunication that is using short guard intervals. The wireless devicebegins to decode the preamble to determine the guard interval type andother configuration parameters of the communication while stillreceiving additional portions of the communication after the preamble.However, by the time the wireless device determines the guard intervaltype, part of the first data symbol after the short guard interval mayalready have been received. Thus, the wireless device experiencesdifficulties processing the communication due to the lag time fordecoding the preamble.

Therefore, in one embodiment, the transmitting device will transmit thecommunication with a long guard interval for a first data symbol in thecommunication and transmit subsequent data symbols in the communicationwith short guard intervals. In this way, a receiving wireless device candetermine a type of guard interval used for the subsequent data symbolswhile always processing the first data symbol with a long guardinterval. In another embodiment, instead of always processing the firstguard interval as a long guard interval, the receiving device buffersthe communication until the guard interval type has been determined.Once the guard interval type is known, the receiving device can processthe buffered communication according to the determined guard intervaltype.

Embodiment 1 Long Guard Interval Followed by Short Guard Interval

With reference to FIG. 1, one embodiment of a wireless communicationdevice 100 is shown that is associated with processing single streamcommunications with a short guard interval and greenfield preamble. Thewireless communication device 100 may include a receiver 110 with anantenna 110A, interval select logic 120, and a signal processor 130. Inone embodiment, the receiver 110 is configured to receive wirelesscommunications from a remote device 140. The remote device 140 is, forexample, a wireless network interface card (NIC) that includes anantenna 140A. The remote device 140 may be integrated in a wirelessaccess point, a laptop computer, a smartphone, a tablet computer, and soon. Additionally, the wireless communication device 100 is, for example,a computer, a smartphone, a tablet computer, a laptop, a wireless accesspoint, a network interface card (NIC), and so on.

The remote device 140 provides a communication to the wirelesscommunication device 100 in the form of a radio frequency (RF) signal.In one embodiment, the RF signal is, for example, a sub 1 GHZ signal, asignal that is generated to be compatible with an implemented standard(e.g., IEEE 802.11ah, IEEE 802.11n, IEEE 802.11ac, and so on), a signalthat is compatible with 3^(rd) generation mobile telecommunications(3G), a signal that is compatible with 3GPP Long Term Evolution (LTE),and so on.

In one embodiment, the radio frequency signal is encoded according toorthogonal frequency-division multiplexing (OFDM). Thus, the remotedevice 140 transmits an OFDM signal to the wireless communication device100 to provide the communication. In one embodiment, the OFDM signalincludes a preamble followed by a plurality of data symbols. The remotedevice 140 may use a greenfield preamble in the communication. Agreenfield preamble is a type of preamble that does not account forcompatibility with legacy devices. Greenfield preambles use lesstransmission overhead (e.g., fewer bits) because additional bitsrequired for compatibility with legacy devices are not included.Accordingly, greenfield preambles may be used with high-throughputcommunications such as multi-stream communications (e.g., MIMO 802.11ncommunications). However, multi-stream communications add to thecomplexity of the preamble since more fields for providing configurationinformation about the multiple streams are included. Thus, the remotedevice 140 may be configured to also use greenfield preambles withsingle stream communications.

In one embodiment, the interval select logic 120 is configured todetermine whether the OFDM signal is a single stream communication inorder to, for example, know whether determining the guard interval typeis time-sensitive. Thus, the interval select logic 120 may control thesignal processor 130 to process a data segment of the OFDM signalaccording to a pattern of a long guard interval followed by a determinedguard interval type (e.g., long or short) for remaining data symbols ofthe data segment. Additionally, the interval select logic 120 may alsocontrol the signal processor 130 to process multi-stream communicationsaccording to the same pattern of a long guard interval in a data segmentfollowed by a determined guard interval type (e.g., long or short) forremaining data symbols of the data segment.

In another embodiment, when the communication is a single streamcommunication, the type of guard interval is always short. Thus theinterval select logic 120 is configured to determine whether thecommunication is a multi-stream communication or a single streamcommunication to determine the guard interval type. Accordingly, if theOFDM signal is a single stream communication, the interval select logic120 may control the signal processor 130 to automatically process a datasegment of the OFDM signal according to a pattern of a long guardinterval followed by short guard intervals for the remaining datasymbols of the data segment.

One example of difficulties (e.g., processing delays) that may arisewhen using short guard intervals with single stream communications isillustrated with respect to FIG. 2. FIG. 2 illustrates a time axis injuxtaposition to an exemplary multi-stream communication 200 and anexemplary single stream communication 210. The multi-streamcommunication 200 includes a greenfield preamble 205 that is followed bya data segment 240. In one embodiment, the data segment 240 includes aplurality of data symbols that are each preceded by a guard interval.The greenfield preamble 205 includes a short training field (STF) 220, afirst long training field (LTF1) 225, a signal (SIG) field 230, and oneadditional LTF field 235 for each additional stream beyond the first.The single stream communication 210 includes a greenfield preamble 215with the same fields 220, 225, and 230 as in the multi-streamcommunication 200. To simplify the comparison, the single streamcommunication 210 is shown with the same data segment 240 as in themulti-stream communication 200. However, the greenfield preamble 215does not include the additional LTFs 235 since there is only a singlestream in the communication 210. It should be noted that while notdiscussed in detail, the preambles 205 and 215 also include one or moreguard intervals. For example, the preambles 205 and 215 can include longguard intervals before each field, i.e., one before each field 220, 225,230, and 235. However, the long guard intervals of the preamble are notthe focus of this disclosure and will not be discussed in detail.

In one embodiment, the SIG field 230 of the preamble 215 includes a setof configuration parameters 231-234. The set of configuration parameters231-234 includes an indicator that specifies the type of guard interval(e.g., field 232) used between symbols of the data segment 240. In thesingle stream communication 210, the SIG field 230 occurs directlybefore the data segment 240. Thus a receiving device has a limited timeperiod to decode a guard interval type from the SIG field 230 prior toreceiving the data segment 240. Accordingly, difficulties with decodingthe SIG field 230 prior to a short guard interval lapsing in the datasegment 240 may occur in single stream communications.

For purposes of comparison, consider that communications 200 and 210 arereceived in parallel in two separate devices. The dashed line 250represents an example point in time during the reception ofcommunications 200 and 210 when the decoding of the guard interval typefrom the SIG field 230 is complete. The dashed line 245 represents wherea boundary between the end of a first short guard interval would occurand where the beginning of data in a first data symbol of the datasegment 240 for the communication 210 occurs. Thus, in a devicereceiving the single stream communication 210 with short guardintervals, decoding of the guard interval type completes, for example,at 250 after the passing of the short guard interval at 245. Bycontrast, the multi-stream communication 200 is still receiving aportion of the greenfield preamble 205 at time point 250 when decodingof the guard interval type completes at time point 250. This time pointis also before a time when the data segment 240 of the multi-streamcommunication 200 with a guard interval having a boundary at 245 evenbegins to be received.

Accordingly, the interval select logic 120 of FIG. 1 is configured tocause the signal processor 130 to process a first guard interval in thedata segment 240 of the single stream communication 210 as a long guardinterval and subsequent guard intervals based on an indicated type inthe SIG field 230 (e.g., short or long). In this embodiment, the remotedevice 140 is also configured to generate the communication according tothis configuration. In other words, the remote device 140 is configuredto generate single stream communications with the first guard intervalof the data segment as a long guard interval and subsequent guardintervals according to a selected guard interval type (e.g., either longor short guard intervals). In this way, the devices may mitigatedifficulties with lag associated with decoding the guard interval typein single stream communications.

Additionally, the interval select logic 120 may be configured todetermine the guard interval type of a communication based on whetherthe communication is a single stream communication since determining theguard interval type is time-sensitive in a single stream communication.The interval select logic 120 is configured to determine that thecommunication is a single stream communication based on, for example,(i) one or more parameters in the SIG field 230 that indicate thecommunication is a single stream communication, (ii) by determining ifthe SIG field 230 is the last field in the preamble prior to the datasegment 240, or (iii) by determining that the SIG field includes a guardinterval type indicator field.

Additionally, the remote device 140 may be configured to provide datasegments for all communications in the format of a long guard intervalfollowed by a selected type of guard interval (e.g., short or long). Forexample, the remote device 140 may generate all data segments 240,whether for single or multi-stream communications, in the format of along guard interval followed by a selected type of guard interval forsubsequent data symbols in the data segment 240; and the selected typeof guard interval may be signaled in the SIG field 230 in the preamble.With continued reference to FIG. 2, consider that the boundary marker245 of communications 200 and 210 now represents a terminal point for along guard interval in the data segments 240. Thus, the data segments240 include a long guard interval followed by guard intervals (notillustrated) of the type denoted by the SIG field 230 (e.g., short orlong). Accordingly, once a guard interval type for a communication(e.g., a packet) from the remote device 140 is known, the intervalselect logic 120 is configured to use the same guard interval type forthe remaining data symbols received from the remote device 140 withinthe same communication.

In one embodiment, the interval select logic 120 is configured todetermine a guard interval type on a per communication basis. That is,the interval select logic 120 determines a guard interval type for eachcommunication (e.g., each packet) received. In another embodiment, theinterval select logic 120 causes the signal processor 130 to process acommunication according to a guard interval type determined from aprevious communication from the same device. Thus, if multiplecommunications (e.g., a plurality of packets) are received from the samedevice, then the interval select logic 120 uses a previously determinedguard interval type for that device. In this way, the interval selectlogic 120 may determine a guard interval type for communications from adevice only once.

Further details of the wireless communication device 100 will bediscussed in conjunction with FIG. 3. FIG. 3 illustrates one embodimentof a method 300 associated with processing a single stream communicationthat includes short guard intervals and a greenfield preamble. FIG. 3 isdiscussed from the perspective that the method 300 is implemented andperformed by the wireless communication device 100 of FIG. 1 todetermine the type of guard interval used in communications sent fromthe remote device 140. In the following discussion, only a single remotedevice 140 is discussed, however, multiple remote devices maysimultaneously communicate with the wireless communication device 100.

At 310, the method 300 begins when the wireless communication device 100receives an OFDM signal from the remote device 140. The wirelesscommunication device 100 progressively receives the OFDM signal from theremote device 140 over a span of time. Thus the entire communication(e.g., packet) embodied by the OFDM signal is not immediately availablefor processing. However, a first segment of the communication includes apreamble with configuration information that is processed whileadditional segments of the communication are received.

Thus, at 320, the wireless communication device 100 determines the guardinterval type of the OFDM signal, for example, from the portion of theOFDM signal that has been received (e.g., the SIG field in thepreamble). Determining the type of guard interval may occur in severaldifferent ways. For example, if the signal is a single streamcommunication then the guard interval may be configured to always be ashort guard interval. Thus, in this example, the method 300 determinesthe guard interval type by determining whether the communication is asingle stream communication. To determine that the signal is a singlestream communication, the wireless communication device 100 may, forexample, determine if a SIG field is i) the last field of the preambleand ii) directly before a data segment, check an indicator field in theSIG field, and so on.

In another embodiment, at 320, the method 300 may determine the guardinterval type by decoding a guard type indicator in the preamble of theOFDM signal (e.g., decoding the SIG field in the preamble of a single ormulti-stream communication). The guard type indicator specifies if thesignal is using a short or long guard interval in the data segment ofthe current communication. In yet another embodiment, at 320, the method300 may determine the guard interval type by first checking if thesignal is a single stream communication and then checking an indicatorin the preamble for a guard interval type.

At 330, the OFDM signal is processed. It should be noted that block 330may occur in parallel or substantially in parallel with block 320. Forexample, as the guard type interval is being determined at 320, thewireless communication device 100 is receiving and begins to process afirst portion of a data segment (e.g., a first OFDM data symbol) of thesignal that occurs after the preamble. When the wireless communicationdevice 100 begins to process the first data segment, configurationparameters from the preamble that describe how the signal is encodedhave not yet been decoded due to, for example, processing delays. Thus,the wireless communication device 100 processes the first data symbol inthe data segment of the OFDM signal according to a predeterminedconfiguration. In one embodiment, the predetermined configurationincludes always processing a first guard interval for the first datasymbol of the OFDM signal as a long guard interval. In this way,processing is not delayed for a first data symbol that is receivedbefore configuration information is decoded.

At 340, the wireless communication device 100 can process subsequentdata symbols based, at least in part, on the determination from block320 of the method 300. It should be noted that when processing the firstdata symbol of the data segment according to a predeterminedconfiguration, the remote device 140 is configured to provide the OFDMsignal according to the predetermined configuration.

FIG. 4 illustrates an additional embodiment of the wirelesscommunication device 100 from FIG. 1 that is configured with separateintegrated circuits and/or chips. In this embodiment, the receiver 110from FIG. 1 is embodied as a separate integrated circuit 410. Theantenna 110A is also embodied on an individual integrated circuit 440.Additionally, the interval select logic 120 is embodied on an individualintegrated circuit 420. The signal processor 130 is embodied on anindividual integrated circuit 430. The circuits are connected viaconnection paths to communicate signals. While integrated circuits 410,420, 430, and 440 are illustrated as separate integrated circuits, theymay be integrated into a common circuit board 400. Additionally,integrated circuits 410, 420, 430, and 440 may be combined into fewerintegrated circuits or divided into more integrated circuits thanillustrated. Additionally, in another embodiment, the signal processor130, the interval select logic 120, and the receiver 110 (which areillustrated in integrated circuits 430, 420, and 410, respectively) maybe combined into a separate application-specific integrated circuit. Inother embodiments, portions of the functionality associated with theinterval select logic 120 and the signal processor 130 may be embodiedas firmware executable by a processor and stored in a non-transitorymemory.

Embodiment 2 Buffering the OFDM Signal while Determining a GuardInterval Type

FIG. 5 illustrates a wireless communication device 500 that includeselements similar to the wireless communication device 100 of FIG. 1. Forexample, similar to the wireless communication device 100, the wirelesscommunication device 500 includes a receiver 510 with an antenna 510A,an interval select logic 520, and a signal processor 530. However,wireless communication device 500 also includes a buffer 540. Thereceiver 510 is configured to receive, for example, communications inthe form of OFDM signals from a remote device such as remote device 550.The remote device 550 is a device that is similar to the remote device140 of FIG. 1.

In one embodiment, the interval select logic 520 is configured todetermine the type of guard interval for a communication. The intervalselect logic 520 may determine the type of guard interval in severaldifferent ways. In one embodiment, the interval select logic 520 isconfigured to determine the guard interval type by decoding a guard typeindicator in the preamble of the OFDM signal. The guard type indicatorspecifies if the signal is using a short or long guard interval by, forexample, the presence of a “1” or “0” bit in the guard type indicatorfield. In another embodiment, the interval select logic 520 isconfigured to determine the guard interval type by first checking if thesignal is a single stream communication and then checking an indicatorin the preamble for a guard interval type.

While the interval select logic 520 is determining the guard intervaltype, the buffer 540 is configured to buffer the incoming OFDM signal.For example, as discussed above with reference to FIG. 2, decoding ofthe guard interval type for the data segment in a single streamcommunication does not complete in time to process the first data symbolin the communication with the indicated guard interval type. Thus, inone embodiment, the receiver 510 is configured to buffer the incomingcommunication in the buffer 540 to provide the interval select logic 520with sufficient time to decode the type of guard interval for thesignal. In this way, the wireless communication device 500 can mitigatethe decoding delay for the guard interval type without the remote device550 generating the communication in a particular way to account for thedelay.

Additionally, the interval select logic 520 is configured to provide theguard interval type to the signal processor 530 upon completing thedetermination of the type. Thus, when the communication is configuredwith a short guard interval, in one embodiment, the signal processor 530is configured to adjust the bit length for the buffered data symbol toaccount for the guard interval type.

Further details of the wireless communication device 500 will bediscussed in conjunction with FIG. 6. FIG. 6 illustrates one embodimentof a method 600 associated with processing single stream communicationswith a short guard interval and greenfield preamble. FIG. 6 is discussedfrom the perspective that the method 600 is implemented and performed bythe wireless communication device 500 of FIG. 5 to determine the type ofguard interval used in communications sent from the remote device 550.In the following discussion, only a single remote device 550 isdiscussed, however, multiple remote devices may simultaneouslycommunicate with the wireless communication device 500.

At 610 of method 600, the wireless communication device 500 begins toreceive a communication in, for example, the form of an OFDM signal fromthe remote device 550. At 620, the wireless communication device 500buffers the OFDM signal as it is received. In one embodiment, blocks610, 620 and 630 occur substantially in parallel. For example, at 630,as the wireless communication device 500 determines if the guardinterval type is a short guard interval, the OFDM signal is also beingbuffered as it is received. Accordingly, by buffering the communicationthe wireless communication device can defer processing the communicationuntil configuration parameters from the preamble are identified. Theconfiguration parameters include the guard interval type and, forexample, information that indicates whether the communication is asingle stream communication, a type of encoding used with thecommunication, and so on.

If the communication is encoded using a short guard interval, thenmethod 600 proceeds to 640. At 640, the wireless communication device500 adjusts, for example, a bit length for the guard interval of thebuffered data symbol to be compatible with the short guard interval. Inone embodiment, when the communication is configured with short guardintervals, processing of the signal may be modified from a defaultinterval (e.g., a long guard interval) to a shorter span so that a firstportion of the data symbol is not lost or incorrectly processed as beingpart of the long guard interval.

Accordingly, at 650, the wireless communication device 500 can process afirst data symbol in the OFDM signal after the encoded guard intervaltype is known. In this way, processing difficulties with lag time indecoding a preamble of the OFDM signal can be avoided.

FIG. 7 illustrates an additional embodiment of the wirelesscommunication device 500 from FIG. 5 that is configured with separateintegrated circuits and/or chips. In this embodiment, the intervalselect logic 520 from FIG. 5 is embodied as a separate integratedcircuit 720. Additionally, the receiver 510 is embodied on an individualintegrated circuit 710. The antenna 510A is also embodied on anindividual integrated circuit 750. The signal processor 530 and thebuffer 540 are also embodied on individual integrated circuits 730 and740 respectively. The circuits are connected via connection paths tocommunicate signals. While integrated circuits 710, 720, 730, 740, and750 are illustrated as separate integrated circuits, they may beintegrated into a common integrated circuit board 700. Additionally,integrated circuits 710, 720, 730, 740, and 750 may be combined intofewer integrated circuits or divided into more integrated circuits thanillustrated. Additionally, in another embodiment, the interval selectlogic 520, the signal processor 530, and the buffer 540 (which areillustrated in integrated circuits 720, 730, and 740, respectively) maybe combined into a separate application-specific integrated circuit. Inother embodiments, portions of the functionality associated with theinterval select logic 520, the signal processor 530, and the buffer 540may be embodied as firmware executable by a processor and stored in anon-transitory memory.

The following includes definitions of selected terms employed herein.The definitions include various examples and/or forms of components thatfall within the scope of a term and that may be used for implementation.The examples are not intended to be limiting. Both singular and pluralforms of terms may be within the definitions.

References to “one embodiment”, “an embodiment”, “one example”, “anexample”, and so on, indicate that the embodiment(s) or example(s) sodescribed may include a particular feature, structure, characteristic,property, element, or limitation, but that not every embodiment orexample necessarily includes that particular feature, structure,characteristic, property, element or limitation. Furthermore, repeateduse of the phrase “in one embodiment” does not necessarily refer to thesame embodiment, though it may.

“Logic”, as used herein, includes but is not limited to hardware,firmware, instructions stored on a non-transitory medium or in executionon a machine, and/or combinations of each to perform a function(s) or anaction(s), and/or to cause a function or action from another logic,method, and/or system. Logic may include a microprocessor programmedwith an algorithm based on the disclosed methods, a discrete logic(e.g., ASIC), an analog circuit, a digital circuit, a programmed logicdevice, a memory device containing instructions, and so on. Logic mayinclude one or more gates, combinations of gates, or other circuitcomponents. Where multiple logics are described, it may be possible toincorporate the multiple logics into one physical logic. Similarly,where a single logic is described, it may be possible to distribute thatsingle logic between multiple physical logics. One or more of thecomponents and functions described herein may be implemented using oneor more of the logic elements.

For purposes of simplicity of explanation, illustrated methodologies areshown and described as a series of blocks. The methodologies are notlimited by the order of the blocks, as some blocks can occur indifferent orders and/or concurrently with other blocks from those shownand described. Moreover, less than all the illustrated blocks may beused to implement an example methodology. Blocks may be combined orseparated into multiple components. Furthermore, additional and/oralternative methodologies can employ additional blocks that are notillustrated,

To the extent that the term “includes” or “including” is employed in thedetailed description of the claims, it is intended to be inclusive in amanner similar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim.

While example systems, methods, and so on have been illustrated bydescribing examples, and while the examples have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe systems, methods, and so on described herein. Therefore, thedisclosure is not limited to the specific details, the representativeapparatus, and illustrative examples shown and described. Thus, thisapplication is intended to embrace alterations, modifications, andvariations that fall within the scope of the appended claims.

What is claimed is:
 1. A wireless communication device, comprising: atransmitter configured to generate an orthogonal frequency-divisionmultiplexing (OFDM) signal that comprises (i) a preamble and (ii) a datasegment, wherein the data segment follows the preamble, and wherein thedata segment includes a plurality of data symbols that are eachrespectively preceded by a corresponding guard interval, wherein (i) afirst guard interval preceding a first data symbol in the data segmenthas a first duration of time, and (ii) each of the corresponding guardintervals that precede the remaining data symbols subsequent to thefirst data symbol in the data segment have a second duration of time,wherein the second duration of time is shorter than the first durationof time, wherein the preamble is a greenfield preamble, wherein thetransmitter is configured to generate the OFDM signal with a signal(SIG) field as a last field of the preamble to indicate (i) that thedata segment is arranged with the first guard interval having the firstduration and the second guard interval having the second duration oftime that is shorter than the first duration of time and (ii) that theOFDM signal is a single stream communication.
 2. The wirelesscommunication device of claim 1, wherein the transmitter is configuredto generate the OFDM signal with one of a mixed pattern or a uniformpattern depending on a type of OFDM signal.
 3. The wirelesscommunication device of claim 1, wherein the OFDM signal is a first OFDMsignal transmitted to a remote device, and wherein the transmitter isconfigured to generate subsequent OFDM signals to the first OFDM signalbased, at least in part, on a type of guard intervals for the first OFDMsignal.
 4. A method, comprising: generating an orthogonalfrequency-division multiplexing (OFDM) signal that comprises (i) apreamble and (ii) a data segment, wherein the data segment follows thepreamble, and wherein the data segment includes a plurality of datasymbols that are each respectively preceded by a corresponding guardinterval, wherein (i) a first guard interval preceding a first datasymbol in the data segment has a first duration of time, and (ii) eachof the corresponding guard intervals that precede the remaining datasymbols subsequent to the first data symbol in the data segment have asecond duration of time, wherein the second duration of time is shorterthan the first duration of time, wherein the preamble is a greenfieldpreamble, wherein generating the OFDM signal includes generating asignal (SIG) field as a last field of the preamble to indicate (i) thatthe data segment is arranged with the first guard interval having thefirst duration and the second guard interval having the second durationof time that is shorter than the first duration of time and (ii) thatthe OFDM signal is a single stream communication; and transmitting theOFDM signal over a wireless communication medium using a transmitter. 5.The method of claim 4, wherein generating the OFDM signal includesgenerating the OFDM signal depending on a type of guard intervals in theOFDM signal.
 6. The method of claim 4, wherein generating the greenfieldpreamble includes generating the greenfield preamble with the SIG fieldhaving an indicator that specifies a type of guard interval used betweenthe data symbols of the data segment.
 7. The method of claim 4, whereinthe OFDM signal is a first OFDM signal transmitted to a remote device,and wherein subsequent OFDM signals to the first OFDM signal aregenerated based, at least in part, on a type of guard intervals for thefirst OFDM signal.
 8. A device comprising: a transmitter configured togenerate an orthogonal frequency-division multiplexing (OFDM) signalwith a greenfield preamble and a mixed pattern of guard intervals thatincludes a first guard interval in the OFDM signal as a long guardinterval and subsequent guard intervals in the OFDM signal as shortguard intervals, wherein the transmitter is configured to generate theOFDM signal with the mixed pattern of guard intervals when the OFDMsignal is a single stream communication, wherein the transmitter isconfigured to generate the OFDM signal with a signal (SIG) field as alast field of the greenfield preamble to indicate (i) that a datasegment is arranged with the first guard interval having a firstduration of time and the second guard interval having a second durationof time that is shorter than the first duration of time and (ii) thatthe OFDM signal is a single stream communication.
 9. The device of claim8, wherein the transmitter is configured to generate the OFDM signalwith one of the mixed pattern or a uniform pattern depending on a typeof OFDM signal.
 10. The device of claim 8, wherein the OFDM signalfurther comprises a plurality of data symbols in the data segmentfollowing the greenfield preamble, and wherein the transmitter isconfigured to generate the OFDM signal by generating a first data symbolof the plurality of data symbols as a data symbol with a long guardinterval, and generating subsequent data symbols of the plurality ofdata symbols based on a selected type of the guard intervals accordingto a type of the OFDM signal.
 11. The device of claim 8, wherein theOFDM signal is a first OFDM signal transmitted to a remote device, andwherein the transmitter is configured to generate subsequent OFDMsignals to the first OFDM signal based, at least in part, on a patternof guard intervals for the first OFDM signal.